Thermoresponsive snap switch having separate ceramic heater means



March 16, 1965 w. B. ALMASSY 3,

THERMORESPONSIVE SNAP SWITCH HAVING SEPARATE CERAMIC HEATER MEANS FiledJune 1, 1962 I NVENTOR. Mum/r75. 4; mm)

ATTORN E Y5 United States Patent 3,174,015 THERMORESPONSIVE SNAP SWITCHHAVING SEPARATE CERAMIC HEATER MEANS William B. Almassy, Pine Brook,N.J., assignor to Tung- Sol Electric Inc, a corporation of DelawareFiled June 1, 1962, Ser. No. 199,443 1 Claim. (Cl. 200-122) The presentinvention relates to expansible wire controlled snap switches, moreparticularly to the type wherein an expansible wire moves the free endof a snap memher to different circuit controlling positions with a snapaction, and comprises a novel switch of this type which is simple toconstruct, precise in operation, of long useful life and of a wide fieldof application. The new switch, which may be operated as a flasher, arelay, a time switch, an overload protector or a. voltage regulatordepending upon the circuit conntctions, is an improvement over the wirecontrolled snap switch disclosed and claimed in Schmidinger Patents No.2,761,931 dated September 4, 1956, and No. 3,037,102, dated May 29,1962.

Like the switches of the above mentioned Schmidinger patents, the newswitch comprises a metal strip adapted to be mounted at one end andcarrying one or more contacts at its free end, the strip being providedwith two generally longitudinal slots which terminate short of the endsof the strip and define a central vane. The central vane is biased atboth ends, and a pull wire, which is secured to the strongly biasedsection of the vane adjacent the fixed end of the plate, extendssubstantially parallel to the strip to hold the vane in compression. Thebias of the two ends of the vane is such that the vane assumes a naturalbow shape before the wire is tensioned. When the wire is tensioned, thevane assumes the form of a. generally M-shaped curve with the initiallyunstressed intermediate portion of the vane forming the depression ofthe M. During operationof the switch, the radii of curvatures of theparts of the vane vary in magnitude but not in sign. One or more fixedcontacts or stops are positioned adjacent the free end of the strip forengagement therewith, the free end snapping into and out of contactclosing position with change in tension in the pull wire.

The new switch differs from that of the Schmidinger patents, however, inthat the change in tension in the pull wire is not brought about as aresult of passage of current through the pull wire. Instead, a separateheater, consisting of a :ceramically coated highly resistive wirewrapped around the pull wire, is provided. Indirect heating of the pullwire in this manner has many advantages. F

For instance, the variations in the period of the snap cycle or rate,and variations in atio, or dwell time in each of the circuit controllingpositions are much smaller with this indirectly heated unit. Further,the consumption of electrical energy is approximately one fourth that ofa unit with a directly heated pull wire and the new switch has shownincreased load carrying capacity and an unusual stability withvariations in load when compared with comparable switches with directlyheated pull wires. In addition, the insulating ceramic bead shown in theSchmidinger patents may be eliminated since the pull wire does not formpart of the electrical circuit, and a ballast resistor and heat baffleare not necessary with the present device.

For a better understanding of the invention and of a switch embodyingthe invention reference may be had to the accompanying drawing of which:

FIGS. 1 and 2 are respectively front and side views of the new switch;and

FIG. 3 is a cutaway side view of an adjusted switch connected in acircuit with a lamp and a power supply.

In the illustrated embodiment of the invention, a rec- 3,174,015Patented Mar. 16, 1965 tangular plate 2 is provided with two slots 4-4which extend for the major length of the plate. The slots 4-4 define acentral vane 6 which varies in width from a minimum adjacent the centralsection to a maximum at the closed ends of the slots. Each side portion8 of the plate is provided with a crimp 10 which shortens its lengthrelative to that of the central vane 6. One end 12, which when the plateis mounted becomes the free end of the plate, is formed with a centralraised section 14 which merges into the adjacent end of the central vane6. This raised portion 14 provides the bias at the free end of the plateand insures against reversal of curvature of the central vane duringoperation of the device. The raised portion or bias 14, in conjuctionwith the crimps 10, causes the adjacent end of the central vane to curveoutwardly from the body of the plate. The metal of the plate adjacentthe other end of the central vane 6 is also forced outwardly away fromthe plane of the plate as indicated at 16 to provide a bias at that endof the plate which likewise insures that the strip adjacent that endwill bow outwardly from the plane of the plate. Preferably, as shownbest in FIG. 1, the width of the central vane 6 is slightly greater atthe end adjacent the bias 16. This end of the plate is welded orotherwise secured to a frame element 18 of the switch and the other orfree end of the plate carries a contact member 20. An L-shaped anchormember 22 of round stock has one leg welded to the convex side of thevane 6 adjacent the fixed end of the plate with its other legupstanding. The frame 18 has a finger 26 bent out therefrom with thefree end of the finger in general alignment with the upstanding end 24of the anchor member. An expansible pull wire 28 is se cured undertension to the finger 26 and to the upstanding end 24 of the anchormember. The pull wire is provided with an insulated heating wire 30which is wound around it. The difficulty in using such an insulatedheating wire is that the insulation prevents the transfer of heat to thepull wire and it was diflicult to obtain units for automobiles thatwould start flashing in less than 4 to 5 seconds after the applicationof current to the heating wire. The present device overcomes this by theuse of a thin ceramic coating 32 which is applied to the wire forinsulation. In the illustrated embodiment the heating Wire is a highresistance wire 34 approximately .00275" in diameter, made out of analloy composed of 73% nickel, 20% chromium and the balance aluminum andiron. An example of such an alloy is Karma produced by Driver-Harris Co.As for the insulation, a quartz coating .0006 thick was found to givegood results. With this quartz coating the flashing operation startedwithin 1.5 seconds after current was applied to the heating wire and theinsulated coating showed high resistance to peeling during winding andhandling operations.

After mounting the snap plate on the frame element and attaching thepull wire tau-t between the anchoring finger 26 and the upstanding leg24 of the L-shaped anchor member, the switch is adjusted by bending ormoving the finger 26 to increase the tension in the pull Wire. Theintroduction of tension into the pull wire through movement of theL-shaped anchor member on the vane, provides a longitudinal pull on thecentral vane which causes the intermediate central section of the vaneto go into concavity while the end sections of the vane remain inconvexity. In this position pressure begins to build up between contact20 and a contact 36 which is fixed to the support 18. When the tensionis further increased by movement of the finger 26, sufficient force isprovided to cause the central portion of the vane 6 to pass beyond theplane of the plate and assume the contour of a relatively flat M. At agiven tension in the pull wire the central part of the plate is forcedthrough a position of unstable equilibrium at'which instant some of theforce accumulated in the vane by the longitudinal pull of the wire isreleased and operates to snap the free end of the plate with the contactaway from contact 36.

A switch so adjusted maybe connected in a circuit such as that showndiagrammatically in FIG. 3. As shown in that figure the fixed contact36, which is insulated from the frame, is connected to a grounded sourceof positive potential indicated by the plus sign. The frame 18 andthemetal plate 2 welded thereto are connected through a load 38,illustrated as a lamp or lamps to be flashed, toground. The heating wireis coupled between the fixed contact 36 and the plate 2 so it isconnected in series with the lamp load 38 across the grounded source ofpositive potential. Thus current flows through the lamp load 38 and theheating wire, and though this current is insufficient to light the lamp38, it will cause the heating wire 30 to heat the pull wire 28 andpermit it to expand. Expansion of the pull wire releases the tensiontherein sufficiently to permit the plate 2 to snap to close contacts 20and 36. With the contacts closed the heating wire 32 is shunted from thecircuit and current flows directly from the contact 36 through the plate2, frame 18 and the lamp 38 to ground. With the heating wire 30 out ofthe circuit, the current through the lamp is sufiicient to light it.Also with shunting of the heating wire 30 the pull wire 28 startscooling and contracting. With contraction, tension in the pull wirereturns to its initial value causing the plate 2 to snap contact 20 awayfrom contact 36 putting the heating wire again in the circuit andreturning the snap switch to its initial position.

The switch is supported on a base 40 of insulating material, such asphenol formaldehyde resin, in which are anchored two prong terminals 42and 44 by means of lugs or tongues which extend through the base 40. Theframe 18 has an offset lower portion 46 which rests on the base 40 overthe terminal 42 and is clamped to the base by the lugs 48 of thatterminal. The frame is provided with a generally square opening 56within which a support 52 for the fixed contact 36 is disposed. Support52 includes a lower generally square plate element 52:: which is clampedto the lower part of frame 18 by inturned flanges 54 of the frame,spacers 56 of mica or the like on each side of the palte elementelectrically insulating the element from the frame. The contact 36 iswelded to one face of the support 52 within the opening of the frame. Arearwardly extending tab 52b on the support 52 provides means foradjusting the position of the fixed contact. For electrical connectionof the contact 36 to the terminal 44 and the heater winding 30, thesupport 52 is provided with an outwardly extending finger 52c.

Also clamped between the flanges 54 and electrically insulated therefromand from the plate element 52a by mica spacers 56, is a plate element58a forming a lower extension of a support arm 58 for a stop 60. Thestop 60 is aligned with contact 36 and has an outwardly extending tab531) thereon for adjustment of the spacing of the stop from the snapplate 2. The upper end of frame 18 is formed along its sides withportions 62 olfset from the plane of the frame to provide spaced areasin which the snap plate 2 is welded. The lower end of the snap plateextends between the contact 36 and stop 60 with the plate carriedcontact 20 aligned with the contact 36. A suitable cover (not shown inthe drawing) is crimped to the periphery of the base 42 to complete theassembly.

In use, the grounded source of positive potential is connected through asuitable switch to terminal 44 and the load 33 is connected to terminal42. Operation of the device so connected has been discussed previouslywith respect to FIG. 3 and a further discussion of it at this time isdeemed unnecessary.

The improved heater of the invention and of a specific flasherconstruction embodying the same has now been described. Obviouslyvarious features of the described flasher could be changed withoutdeparting from the spirit of the invention or the scope of theaccompanying claim.

The following is claimed:

In a snap switch of the type comprising: a frame; two spaced apart stopsattached to said frame; a resilient metallic strip having one endfixedly secured to the frame and the other end freely movable betweenthe spaced apart stops, said strip having two substantially longitudinalslots therein which define a bowed centrally located vane; andexpansible pull wire which is tensioned between the frame and the stripto hold the centrally located vane in compression so that the stripcontacts the first of the spaced apart stops when the pull wire is coldand contacts the second of the spaced apart stops when the pull wire isheated and expands; and a heating wire wrapped around the pull wire tocause its expansion, the improvement which comprises a thin quartzcoating for said heating wire for electrically insulating each portionof the heating wire wrapped around the pull wire from the pull wire andfrom each adjacent portion of the heating wire wrapped around the pullwire, said thin quartz coating being substantially thin with respect tothe heating wire whereby electrical shorts in the heating wire areprevented but rapid heating of the pull Wire is obtained.

References Cited in the file of this patent UNITED STATES PATENTS2,133,309 Schmidinger Oct. 18, 1938 2,272,976 Geer Feb. 10, 19422,761,931 Schmidinger Sept. 4, 1956 2,842,642 Colombo et al. July 8,1958 3,002,077 Caliri Sept. 26, 1961 3,007,026 Woodling Oct. 31, 19613,037,102 Schmidinger May 29, 1962 FOREIGN PATENTS 687,294 Great BritainFeb. 11, 1953

